The frequency of signals associated with integrated circuits (ICs), whether generated within an IC or exchanged with devices external to the IC, has steadily increased over time. As IC signals reach radio frequency (RF) ranges exceeding a gigahertz, it becomes viable to implement inductor structures within ICs. Implementing an inductor within an IC, as opposed to using an external inductor device, typically reduces the manufacturing and implementation costs of the system requiring the inductor. IC inductors can be implemented within a variety of RF circuits such as, for example, low noise amplifiers (LNAs), voltage controlled oscillators (VCOs), input or output matching structures, power amplifiers, and the like.
Although IC inductors are advantageous in many respects, IC inductors introduce various non-idealities into a system that are not present with external or discrete inductors. For example, an IC inductor is typically surrounded by other semiconductor devices that can generate noise. As IC devices reside over a common substrate material that is conductive, signals and noise generated by an IC device can couple into an IC inductor built over the common substrate material.
Another non-ideality of an IC inductor can include parasitic capacitances that exist between the substrate layer and the metal interconnect layer(s) used to form the IC inductor. Although IC inductors typically are built using one or more metal interconnect layers that reside farthest from the substrate layer, finite parasitic capacitances exist between the substrate layer and the metal interconnect layer(s). These parasitic capacitances facilitate coupling of signals between the IC inductor and the substrate layer.
Yet another non-ideality of IC inductors relates to electric fields. Coupling of the electric fields of an IC inductor can induce eddy currents within the substrate layer. The eddy currents can generate losses that reduce the quality factor, or so called “Q,” of the IC inductor.